Proteolytic degradation is a naturally occurring process in all biological kingdoms. Proteolytic degradation also complicates scientific investigation if one wants to examine the undegraded level of proteins. Determination of intracellular protein or membrane proteins is particularly complicated by proteolytic degradation, as the cell lysing process also releases proteases. A variety of protease inhibitors exist for inhibition of proteolytic degradation, and such conventional inhibitors are known to those of ordinary skill in the art. However, when the effectiveness of known protease inhibitors is not sufficient to halt the proteolytic degradation of a protein of interest, or addition of these inhibitors only accelerated proteolytic degradation, one would have to find an alternative way to arrest this problem.
An example of the type of investigation that is complicated by proteolytic degradation is the accurate determination of protein in biological fluid. Such protein determination may also be useful to assess the clinical relevance of therapy via determination of the protein specifically induced by the species of interest.
For example, it is important to evaluate the clinical efficacy of interferon therapy, which is both costly and increasingly popular in the treatment of such conditions as hemangiomas in children, genetically predisposed multiple sclerosis, autoimmune diseases, certain types of cancer, and AIDS. Assaying the circulating level of interferon is technically difficult. However, by assaying an intracellular protein called Mx protein induced specifically by interferon, the efficacy of interferon therapy may be assessed. In a paper entitled, "A Whole Blood Immunoassay for the Interferon-Inducible Human Mx Protein", by Towbin, et al., Journal of Interferon Research, 12, 67 (1992), the authors describe an assay procedure for Mx protein in whole blood cell lysates using an enzyme immunoassay.
Although strides in interferon research in general and Mx protein investigation in particular have been made, it remains a goal to determine the uncompromised level of Mx protein by minimizing proteolytic degradation of Mx protein in evaluating the new application of interferon therapy.
Accordingly, it is an object of the present invention to provide a method of inhibiting proteolytic degradation of an intracellular protein, i.e., Mx protein in cell lysates. It is still another object of the invention to provide an artificial matrix solution whereby an intracellular protein can be kept stable against proteolytic degradation at a temperature at or below 4.degree. C. for at least three weeks.